The present invention relates to a method of preventing deterioration of magnetic characteristics of ferromagnetic metal of alloy particles which are obtained by a reduction in a liquid phase.
When boron hydride such as sodium boron hydride is added to a solution containing ferromagnetic metal ions such as iron, cobalt and nickel ions, the reaction is vigorously performed to precipitate black ferromagnetic metal or alloy under generating hydrogen gas. It has been known that when the reaction is performed in magnetic field, the ferromagnetic acicular particles extended to the direction of magnetic field. Recently, the demand of high density magnetic recording medium has been increased, and the demand of acicular metal or alloy particles which are obtained by said method has been increased.
The inventors have previously invented and proposed the process for effectively preparing ferromagnetic metal or alloy particles by said method.